Greetings!

As for the back button and the pops...

Do you have any signs of disk or memory problems on your player? Are you running hijack, using the reservecache flag in config.ini or running third party software?

I suspect that the 18second glitch and sudden change in volume might be related to the amount of music in the buffer, and a sudden shift to having to access data again. Do you use the autovol settings of hijack at all?

I also suspect that the situation with your going back to the previous track may also be related to a memory issue (flushing the buffer) or a disk issue.

It might be a good idea to run a memory test on the unit, just to be safe. Also, you might want to run a manual fsck and not any errors that you might see.

Lastly, if you are running any third party software or reserving cache memory, try unloading / changing the settings to see if your symptoms change as well.