Thumping is a bad ram, or a dry joint on the one pin of the RAM, the audio processor or a through hole joining the RAM to the processor. Most likely is the RAM though, a single bit error will make that noise. Poor tracking is often a worn laser diode though, it will have a lower power output, and with a worn mechanism and poor tracking it will struggle. Run through the power setup and adjust it. With Sony units those small capacitors are rather infamous for dying, especially the ones under 6V. those really need to be replaced with new ones, buy new stock rather than 20 year old ones, they are likely to last longer.