Ouch, that's a definate no no in the unwritten rules of matedom.
Lesson learned.
If it's a good mate, just let him/her know, and then don't lend them stuff again!

, all my mates are bang on but but I've learned over the years not to trust any of them with ANYTHING, haha, I'll either never see it again or get it back in crappy *** condition.
I got a weird grinding/cd crunching noise on a new premium 3 days after I bought the console (not dropped or anything, not moved while on etc), and then usually disk errors accompanying it, no visible marks/scratches on the game disk though when it happened (thank god), so I've kept it (i'm lazy

) and it's been pretty good ever since (3 months), but if it was a common thing I'd just going to take it back to the retailer.
Hard to know what went on with your console in the time the other fella had your console (maybe he put it in the dishwasher to try and clean it

), but just to let ya know what you're describing happened on my 3 day old premium which hadn't been dropped/misused in the slightest.