Hey I've got a JCM800 1987, it was slightly noisy so I decided to replace the caps, replaced the bias caps and the power filter caps, also replaced the pre-amp tubes and power amp tubes and biased it up. Well it's a lot less noisy in terms of background noise but when i turn up the volume it starts to pickup this really high pitched squeel like some component is screaching in the amp. this doesn't happen when I turn the amp up without anything plugged into the front, so if i have my guitar unplugged and I turn the amp up loud, it's totally fine little noisy but quite acceptably so. this seems to me like it's something in the pre amp? when i hit the choke with a pencil when the amp is on it makes a crunchy noise sometimes and when i touch any component inside the amplifier whilst it's on it echos, pickups this bassy frequency and starts to amplify it. really quite confused.