Problem with Mark IV - power tubes, maybe?

[weemies]

I just received my MKIV today. I've played it for a while and it sounds fabulous. However, I'm having a problem that I've only noticed while recording. Check out this clip:
http://media.putfile.com/Problem-with-Mark-IV

You don't need to comment on the "playing" or the tone, because I just wanted to demonstrate the problem. When I hit the strings hard, there's this awful harsh sound at the beginning of each hit.

This is what I've diagnosed so far:
The problem only happens when I have the MKIV channel volumes very low and the output volume higher. When the output volume is almost at 0, and the channel volumes almost cranked, the problem isn't there. I've only noticed the problem on channel 2 and the lead channel. I should mention that I've been playing pretty much at bedroom volume only. That might be the reason why I can only hear the problem when recording.

I've tried playing with two guitars - the guitar isn't the problem. I've also tried recording with two different mic preamps. The mic positions I can't change because I'm in the middle of recording my friend's album with my single recto. With the single recto, the problem isn't there either.

So I think I can pretty safely conclude that the problem is the MKIV. Can anyone tell me what I should try next? Swap out one power tube at a time, and replace with a new one? The MKIV seller included two spare power tubes, and two preamp tubes.

Edit: Oh yeah, I should also mention that I'm using tweed power, class A, triode, harmonics.

Edit 2: Ok, my friend just listened to the clip, and he says he can't hear anything strange apart from the off-tune string... To me, this problem is clear as day, and is especially apparent on the last few hits in the clip. Let me know what you think.

 

[Tuna141]

I couldn't really hear anything unusual in the clips either.

Since it only happens when you first strike a note, it probably has something to with the signal clipping. If you're running effects, try disconnecting them.

The other thing I can suggest is try swapping preamp tubes around. If may be that one of the tubes is causing the harsh spike that you hear. I'd start with V1.


Good luck.

 

[weemies]

Thanks for the reply. It's not signal clipping though - the signal is going in very soft, like -24db. I played a clearer clip to my friend and he noticed the problem there.

Anyway, I just switched the amp to full power, and the problem seems to be gone. If the problem persists, I'll post a clip that shows the problem better.