Sound crackle

I got my phone a couple of months ago and everything was going great until today. I was listening music in my car using the auxiliary cable and I started to hear a cracking sound, so I changed the song, the same, tried another cable same result in cd and radio everything seems fine at any volume level. Got home and tried some headphones but being the small size of could only hear some crackle at full volume, so I tried the original ones about the same story... Using the headphones I can't really tell if the crackle is present... ????
So has anyone had this problem or do you have any idea how to check it out?
As I bought it straight from htc.com uk, do you know anything about the warranty as I'm thinking sending it back to them...