Are STM Lenses "completely" silent or more so over other STMs?

I have the 18-135 STM, 55-250 STM and 50 STM lenses. To my surprise, I am finding that I do hear some noise in video play back of the lenses making their focusing adjustments.
On video playback on my computer, if I turn the volume from 30% (my normal volume on my computer) to 75% (not normal by any means) for a video of silent footage, I can hear the lens clicking.

The 18-135 is least audible, 55-250 is loud (clicking mostly) and and the 50 is most loud (a different kind of sound but its there).

What prompted me to even check my 3 lenses was that I was doing some test video's prior to recording an event. I had my 55-250 lens on, video mode, IS on, Auto Focus On, with AF at Tracking, in Manual mode 1/60, 1600 ISO, and f/5. It was at night under HS football lighting and I was at 250mm focused on the band conductor. Histogram at this setting was fine. The tracking locked on the conductor at first but while conductor was moving focus start to hunt. He was lit well but for some reason, it kept hunting. During play back, before the band had started playing, I could hear loud clicking (at normal play back volume) during the focus "hunt".

I just need to set my expectations so I can determine if there is any issue with my camera or a particular lens.

I would post a video but unfortunately I can not as I do not have rights to do so. Hopefully I explained the situation well.

I've had 3 STM lenses: 55-250, 50, and 24-105. The 55-250 was reasonably quiet and slow. The 50 is fast enough, but not quiet. The 24-105 STM is both fast and quiet.

EDIT:
After reading the next post, I realize I currently have an 18-55 STM. Very quiet, reasonable fast.

the ones I have used. the 18-135 was dead quiet, 18-55 was dead silent as well. The 55-250 I have makes zero noise, the 24stm you could hear a tiny bit of the focus motor going same with the 50stm.

sounds like you are using the built in mic. If so, stop.

Yes I am, and while that is a valid point it is also a different topic....I still need to get my expectations in order about these STM lenses.

"I just need to set my expectations so I can determine if there is any issue with my camera or a particular lens. "

Considering that the above is what you set in bold, your set up is vitally important and not at all a different topic.

I'd wager you could put an off camera mic very close to the lens and determine that the lens is "completely silent" but that there are no lenses that are "completely silent" when using the internal mic. Reason being is that the noise heard is actually a vibration traveling through the camera body and not noise traveling through the air between the lens and mic.

I have 3 STM lenses, but only my 18-135 STM has IS. Ignoring any noise that the IS system creates (cant actually hear any) my 40mm f/2.8 seems to be the louder than the 18-135 and 24 f/2.8 STM.

Left Handed Brisket wrote in post #18132378
Reason being is that the noise heard is actually a vibration traveling through the camera body and not noise traveling through the air between the lens and mic.

^^This!

Very likely the case as sound travels quite readily though most solid materials as opposed to an airborne path. Keep in mind that this path may also include some noise due to image stabilization occuring.

If the sound is objectionable you may wish to check out the EF-S 18-135mm USM that came out around last February. It is Canon's first lens to use the Nano-USM AF motor. Canon feels it may represent the best of both worlds (USM & STM). Only time will tell.