We purchased a new heater for our Yellow Bellied Slider as our old one decided it didn't want to exist anymore. We went with a different brand that we found on Amazon as we could get it quicker. It's been alright for the last month or so. (I can't remember when we got it)

This afternoon I noticed it said E1 on the screen which the manual said it had been exposed to air. So we topped up the water.  (It was due anyway) So that's been sorted out.

However, just before we topped up the water it started making a clicking sound. Kind of like small glass marbles gently nocking against each other every second. I moved the heater around and checked the suction cups but everything seemed fine. I checked the manual and it mentioned nothing about sound.

I repositioned it so it was lying down. (The manual said that was okay) it kept making a noise but different sounds. I've uploaded a video of the new sound as I didn't think to record the first one, bit it was similar to the new one but slower.

The heater is hygger. HG-916. It says the actual heater itself is 'Explosion-proof quartz heating tube'.
It's been working fine since we got it and for water changes and stuff but all of a sudden today it started making noises we've never heard before. Even from old heaters we've used.

I will be emailing Hygger and contacting the shop we got it from on Amazon but who knows how long that will take and I wanted some quicker bits of advice.
I've kept it on for now just I case it was because of the E1 warning, which means it was exposed to air.

Sorry if this is the wrong place to ask about this, I wasn't sure. Any help or suggestions would be greatly appreciated.

Heater making noises? Advice needed.