I'm a non-audiophile, wondering what symptoms to listen for to tell me if I have damaged my headphones by playing them too loud.

Most music sounds great, but for SOME songs (not all?), the deep bass has a "whirring" or "puttering" sound to it unless I turn the volume lower than normal. Then the bass sounds fine.

Normal, for me, is NOT very loud by most standards. I can't stand a loud bar or club, for instance. So I'm sure I haven't done any harm with my music volume. BUT I played some sound files in Director that came out REALLY painfully loud for just a moment. This happened several times--and with games and everything I do, there have probably been other instances. I wonder if some of those quick super-loud bursts could have done harm? I really can't tell if the issue is new or not--maybe those songs just didn't come up in rotation before, or I was too busy to notice!

What's a good way to test? Would bass be affected more, or treble, or everything?

My headphones are Sennheiser PX-100s (not expensive, sound great, and fold up small for travel--recommended by someone here).

Thanks for any advice. I'm hoping I haven't hurt anything, and a few songs sounding weird won't kill me :)