my heater makes an odd clunk/glub noise when its on....like a few times and small bubbles come off the end...I did a water change today and was super careful to let it sit after unplugging it and then before I plugged it back in...also before I had the other suction cup all the way at the bottom end of the heater and I noticed there was white markings on the glass under where the suction cup clips to it..... anyways I moved that up so both clips are at the top above the elements. Not sure if I fixed the problem, and I'm kind of wondering if anyone else has experienced this? Also its regulating the temp just fine, its just worrying me a little!! Any input would be helpful!!!! Thanks!