I have just now tried the solution being described here, loosening all the external bolts on my Krell FPB 300. All by hand (no torque wrench) I set them all to a snug but not hard torque. If anything, the noises have gotten worse.
It's a pity there is so little information about FPB construction online. I would like to know if the heatsinks, which are apparently attached to 3 rails along the side of the amplifier, can be completely removed. My initial fear that simply loosening the bolts could cause an electronic failure were apparently unfounded. But taking this one step further and actually removing each heatsink to check and clean the rails behind it, I'm not sure if that can be done safely. I'm pretty sure most noises are caused by small movements of the bolts, heatsinks, and rails under varying stresses caused by differential thermal expansions.
I'm going to continue trying different methods of torquing the bolts for now. I'm getting a wrench to set the torque consistently to some level between 10 lbin to 50 lbin. I can try low and I can try high. Also there's a question of HOW you torque the bolts. For example, should you do it when the amp is cold, when it's idling, or when it's going full blast? It's probably safest to do it wihen the amp is cold, but probably more useful to do it when the amp is idling or hot.
The factory and one other service guy has suggested putting heat conducting tape on the rails. At first, I didn't like that idea at all. But I may ultimately have to get that done. Also I wonder about the washers that were allegedly used on later runs of the FPB series, I wonder if I can add those washers to my unit.
