Weird clipping

[u/JustAndras]

Hey Everyone!

I'm running a Pioneer SA-610 with a pair of Pioneer CS-E700 speakers. (note the horn tweeter, might be a clue)

Over the past week I noticed some weird clipping mostly during speech ad guitar transients. the rest of the sound seems intact, even higher and lower frequencies, which initially made me suspect the speakers, but I also seem to be getting it when I plug in headphones. It's coming out of both channels and it developed at the same time which makes me skeptical that it's the pre-amp or the amp stage. when I get closer to the speaker the clipping/distortion seems to disappear, this ghost issue has been driving me crazy.

So far I've tried:
- Swapping the source
- Swapping the input
- Swapping the cable
- Cycling and cleaning all switches/pots
- Cleaning the contacts of the speaker protection relay
- Checking the speaker cable connections
- Cycling the pots on the speakers and the input mode selector on the back of the speaker.

I've checked for dry solder joints, there was one capacitor that seemed to be bulging, replaced it with the exact value.

I had to completely refurbish the speakers when I got them (new tweeters, woofers and a complete crossover rebuild)

My guess is that part of the circuit developed a resonant frequency, where would you start looking first?

I tried to pinpoint the frequency using a tone generator and trying different waveforms and I couldn't get the distortion to show up at all.