Strange thingie in power cord of used Adcom amp

I just bought a used Adcom GFA 6000 5-channel amp. A small segment of the power cord has been taped into a small loop about an inch and a half in diameter. Inside this loop there is a small, open plastic box containing an even smaller, hollow half-cylindrical piece of metal. The metal looks like a permanent magnet, but does not exert any noticeable magnetic field (it does not attract a nail). The power cord itself is intact with no splices or breaks. The electrical tape simply holds it in a loop around the small metal object.

The seller of the amp tells me that it is a "tloroid" (typo for toroid?) and that it "came that way." He says it reduces interference and noise. To test the amp, I plugged it directly into the wall outlet with no protection or conditioning. All five channels actually sound pretty good driving a KEF 104.2 -- there is no hum or buzz, and only a barely audible hiss with no source playing.

What is this mysterious gadget? Should I leave it in place, or remove it? When the amp goes into my system, the power cord will be plugged into a Monster PowerCenter HTS850.

Thank you.
Sounds like a chuck key holder. Does that power cord have a Black and Decker logo on it? Seriously, I have two Adcom amps (one new) and neither of them came with any power cord accessories. I would just chuck it.
it is a "ferrite filter"
Used to help eliminate AC powerline noise.
Leave it on. It ain't hurting anything, and may help a teeny bit.
You can take it off if it bothers you too. no problem.
I have them on nearly all my source components
Actually, these loops are often a "retlif" ("filter" backwards) and their main purpose is to prevent your equipment from putting noise on the power line. They are often necessary for the equipment to pass muster with regulators.
They're parasites from outer space. The goverment has been trying to hush hush this phenomonon for years. As long as your take appropriate care they cause no harm. On the other hand, if you don't, things can get ugly. BE VERY CAREFULL to dress your cables appropriately. Should your other cables get in contact with them, they will start to breed. Then they will crawl back into your power lines. If they succeed in getting into items such as toasters, well then your at their mercy. Having a ravenous appetite for electricity and being removed from the source, they will overtake your mind to the point where you will crave what they crave, electricity. Remembering where they first recieved this nectar, they will lead you to Hi Fi salon after Hi Fi salon in a never ending search for either sublte delicacies like SET or go on complete binges for mega watt high current bipolars. If you take enough of the appropriate chemicals to help ward off this possibility and then apply black light over these inhabited cords, you can actually watch them dance to the music played through them. They're actually very cute.
Thank you Elizabeth! I searched "ferrite filter" and found exactly the object attached to my amp's power cord. Here is the link:'ferrite%20filter'

Unsound, you show promise as a sci-fi writer. Do you remember the Star Trek TNG episode in which the Enterprise's computer becomes infected with nanites?
Javahip, thanks and no, I'm not a Trekie. How ever, I think it's obvious that I've been infected by ninnies.