A little more tech info about strange sounds in conjunction with ufos from site:
Effects of UFOs Upon People
Shock waves appear to be generated only at take-off. While sitting on the ground, the propulsion system is presumed to be turned off; that is, no
external field surrounds the UFO. Power would then be required to initiate the field. The sudden appearance of mist in the San Joaquin case is a vital
detail. That region in California is noted for very dense, ground fogs resulting from ground cooling due to radiant heat loss to the cosmos during
long winter nights and high humidity near sloughs and swamp s. Water vapor adjacent to the UFO could have been condensed by a reduction either in
temperature or pressure. Because the phenomenon was accompanied by a shock wave, a change in temperature alone can be ruled out. The newly generated
field must have exerted an outward force on the
atmosphere, thereby reducing the pressure close to the surface. A very small pressure change, indeed, would suffice to cross the dew point and
condense water vapor from saturated air at 100% humidity. Such condensation can sometimes be observed in the low-pressure zone above airplane wings.
Again microwaves emanating from UFOs are suspected because, at certain wavelengths, they are resonantly absorbed by water molecules with an
accompanying transfer of momentum, that is, a force. Resonances are at wavelengths of 0.17 cm. with four stronger
ones below 0.1 cm. Continuation of the process of pushing the air out of the way is the likely reason that UFOs can
fly faster than the speed of sound without creating sonic booms.
The most prevalent types of sounds are either low or high pitch. Words used by witnesses often succinctly and specifically denote the pitch. For
example, the former might be approximated by a hummingbird, the latter likened to the squeal between stations on old-fashioned AM radios. Two
revealing cases have recently come to light after being hidden for decades: At 4:00 a.m. on July 25, 1957, several workers were taking a break at the
Daye Steel Plant in Huangshi City, Peoples Republic of China. Upon hearing a humming sound, they noticed a bright spot in the clear night sky that was
increasing in apparent size. As it came closer, it was seen as a circular plate giving off a dazzling white light and leaving a white trail. During a
two- to three-minute observation, it flew over the frightened observers at 1000 m., producing a whistling sound that was louder than a jet. As the
object approached the witnesses, the low pitch changed to high pitch; no mention was made of any intermediate tones.
The next example, collected by the CIA in the southern Belgian Congo in 1952, remained secret until released in
1983 under a lawsuit pursuant to the Freedom of Information Act.
Two fiery objects glided in sweeping curves over uranium mines. They were seen in several perspectives as disks, ovals, and thin lines. During 10 to
12 minutes of observation, they emitted hissing and buzzing sounds. Commander Pierre at a small airfield jumped into a fighter plane and took off in
pursuit. He was able to get within 150 m. of the objects that were disk-shaped, aluminum, 12 to 15 m. in diameter, with a rim of fire. They were
emitting a whistling sound that could easily be heard over the
airplane engine. Note that the sound changed from low pitch to high pitch as the witness approached the objects, without mention of intermediate
tones.8 In both cases, the range closed, with movement of the object in China and of the witness in the Congo.
It has long been recognized that people can hear lectromagnetic radiation in the microwave region, such as radar and microwave radiation from UFOs was
suspected as the cause of humming sounds. Relatively little was known about this phenomenon 15 years ago, but it had been well established that the
aural response was caused by short bursts of energy corresponding to pulsation of the microwave source. In some uncertain manner, the pulses
stimulated the organ in the inner ear that sends signals to the brain. The tonal value perceived by experimental
subjects corresponded to the pulse rage of the source. Also, the location of the source was usually thought to be behind the head as the direct
response of microwave bypassed the time delay of ordinary, slow-moving sound waves reaching the more remote ear. This process, known as binaural
audition, is one of several clues to recognizing the direction from which sounds originate. Vigorous research during the 1970s brought this highly
phenomenon into sharp focus.9 But for the present purpose, many details must be omitted so some statements are subject to various technical
restrictions that are not mentioned. Generally speaking, it has been shown experimentally that people are able to hear pulsed microwaves from 200 to
3,000 MHz with peak power densities of 300 mW/cm2 and average power densities as low as 0.4 mW/cm2 with pulse widths of 1 to 100 microseconds (msec).
As the shape of the response curve is a steep-sided mesa, the range of pulse width is probably about 10 to 40 sec.
In terms of average power density, the threshold is pproximately 120 mW/cm2. Therefore, very low-intensity, microwave radiation pulsed at 50 to 100
cycles per second would be “heard” and aptly described as humming.
Experiments with animals showed that cats were 20 to 30% more sensitive than people, but one dog tested was 5
times more sensitive. That result may explain why agitated dogs are the first indication of many UFO events.
An entirely different mechanism, known as the thermoplastic process, appears to be responsible for the high pitch sounds. Absorption of energy in
biological tissue produces an extremely small increase in temperature. Due to thermal expansion of the tissue, a corresponding increase in pressure is
produced that then propagates through the medium as a sound wave. A microwave pulse impinging upon the head thereby creates a pressure wave that
propagates through the skin, muscle, bone, and brain tissue and reverberates inside the cranium. These vibrations are carried by bone conduction to
register as sound in the auditory nerve. Microprobes have been surgically implanted
in the auditory nerves of animals to measure the frequencies of pulses stimulated by this mechanism. It has been found that the frequency depends only
upon the size of the head and the acoustical properties of brain tissue.
An extremely intricate, theoretical analysis by Dr. James C. Lin accurately duplicates the experimental data for guinea pigs and cats.10 For example,
the calculated frequency for cats ranged from 30 to 40 kHz, whereas the measured value was 38 kHz. The measured value for cats is within their normal
hearing range, up to 60 kHz, but well beyond the limit of human hearing at 20 kHz. The calculated threshold for cats was 589 mW/cm2 for a head radius
of 3 cm.
For a man with a head radius of 7 cm., the calculated frequency range from 10 to 15 kHz based upon theoretical models expected to yield upper and
lower limits. The calculated threshold for man, 2183 mW/cm2, is extremely high compared to safety limits in the U.S. for short-term exposure of only
10 mW/cm2. Anyone hearing a shrill whistle from a UFO would be in serious danger.
Thus, experiment and theory show that the pitch perceived from impinging microwave pulses result from two distinctly different mechanisms. At weak
intensities and pulse rates in the low audio range, the pulses directly stimulate the inner ear and are interpreted as humming sounds. For very
intensive radiation pulses, pressure waves reverberate inside the head creating the impression of high pitch whistles. No known mechanism produces
tones of intermediate frequencies. Thus, the sounds stimulated by microwave radiation from UFOs would be discontinuously
dependent upon the distance to the UFO.