[RFI] Vibrating Ferrite Chokes on Service Line

[Aaron Kreider]

So I finally got around to putting monster chokes on the service line 
that feeds my house and several neighbors.  3 chokes on each line 
(positive, negative, and neutral) with zero turns (as the wire is too 
thick).  It decreased my noise on 492 khz from 50 uV to 42 uV (*probably 
- there is some uncertainity as the level of noise varies presumably due 
to electricity usage  -- currently it is at 62 uV*).

The 492 khz is a 9th harmonic of the 49.5 khz fundamental rfi source.

The unexpected thing was that the chokes vibrated and made a loud 
buzzing noise that can be heard 40 feet away (even over modest street 
noise).  This was very concerning at first, until I looked it up online 
and found that this is normal behavior.

Jim Brown - you might want to include information about choke vibration 
in your very informative guide.  I searched it for "vibrat" and didn't 
find any mention of this phenomena.

Anyways, I removed the chokes - because I'm concerned that the vibration 
would damage the insulation on the service lines.

The chokes also became strongly magnetized, making them harder to open.

The choke on the neutral line vibrated a lot less than the others.

Is it safe to have the vibrating chokes on the service lines?  I took a 
video, but it was low-resolution and I wasn't able to find out what part 
of them is vibrating.  I'm guessing that it is the small gap between the 
two pieces of ferrite - in which case the ferrite might eventually 
break, but it won't cause problems with the service line.  It sounds 
like it might be a 60 hz vibration.

It could also be that the ferrite is vibrating against the service line, 
or the metal is vibrating against the plastic shell on the choke.

I could reduce the vibration with foam or another method.

I might also try putting chokes on the service line on the other side of 
my house, as I'm not sure if the original noise is from the main power 
lines or one of my neighbors (and there are multiple noises - so 
probably at least one of them is from the neighbors). Unfortunately 
access to this other side of the service lines is very difficult.

Aaron