It really depends on the model and board rev but Mark may be right. I would contact Ray and see.
I've had several of the older models (pre-IQ series) that were supposed to be susceptible to the thumps but had none at all. In fact, I've got a basically new 2502IQ that has always had a slight turn-off thump. I also have a 1752S and 2202 that have zero thump noise.