Like stated above check for discoloration or deformities in the plastic make sure your RHP is not getting too hot so temp gun it and the plastic behind it.
If all of this does not pinpoint you may have to add elements to the enclosure one by one over a period of time(An old enclosure setup or even a quarantine setup to store your noodle in while this is happening would be advised) First remove your noodle and then the substrate clean the enclosure. But after you done cleaning DO NOT put more substrate in.
then wait for a few for the smell(How long this goes in depends on the average time it took the smell to come back after deep cleaning.
remove hides and repeat the rest of the above
continue removing elements until it is just the tank and it heating elements and then leave those on.
Continue to do this and then pinpoint the origin of the smell.