(Any Pro Tips?) Roland KC-550 synth amp with strange F# buzz in tweeters?

[phillipla]

Hey guys,

So troubled by my KC550 Roland amp, and decided to post for help.

I have 3x of these amps, and run two of them in stereo to make the most of my effects and stereo imaging. Sounds great.

One of the KC550's has a strange buzz, sizzle, digital interference/cell phone type sound coming from its tweeter only.
It happens most pronounced on F# notes and any octaves of it. With a little bit around that note's frequency and other notes close by.

Ive tried everything since I have access to all 3x and parts that are known working:
- tweeter swap
- woofer swap
- reseating speaker connections
- soldering woofer/tweeter wires straight to terminals
- swap cables, input jacks, placement in room, different outlets, etc

IN all cases the working units with the "bad" parts continue to work great.

So ive narrowed this down to something on the circuit board itself in the buzzing/tweeter sizzle KC550.

What else can I look for on the board? Have you ever seen this, only certain notes clipping like this?

** Also when i remove the woofer and its just tweeter only, no more issues. Introducing the woofer back in, makes the tweeter clip out at the strange frequencies **

Pics and video clip below
https://www.dropbox.com/s/u5gfe98mkk...small.mov?dl=0

[phillipla]

FIXED

In case that this can help anyone in the future, wanted to layout the steps I took

1. An engineer friend of mine said the problem was mechanical/physical since it only creeped up during certain frequencies and loudness. Also some notes around that frequency.
2. Bang on the amp! Try to find the most sensitive area first (wide angle)
3. Use wooden spatula and top on components inside the board until you find the most microphonic/sensitve one
4. 2x capacitors on the lower board were the most sensitive to tapping, I found
5. Disassemble the board and remove
6. Reflow solder to all connections in that area of the board
7. Reconnect and test
8. Problem solved!

* Looks like the area directly behind the speaker magnet is getting more abuse from playing, transport, etc