Audio in- or decrease on its own

Greetings,

I've noticed this for years and still it still hasn't been fixed, that when you work on longer projects with lets say up to a hundred imported pieces of footage, even recorded on the same device, cut those to size and play with the audio Premiere gets weirder and kind of sentient with the audio levels.

For example after only pre cutting up to 90 minutes of footage I imported a new part, played it back = everything is fine. After moving it in the middle of everything, still on the same layer and no effects applied, when I play the audio is suddenly MUCH louder so I have to decrease it -12 DB to get it back to origin level.

This can not be normal but besides that I don't know what other data I can provide to you as this bug is really hard to describe other than that.

On another instance after increasing the volume of single parts for lets say +6 db for the same amount ot footage clips, Premiere auto-quiets future clips more and more the. Like new files are suddenly a lot quieter. Basically the same error as above just the other way around.

Again I'm sorry for this only broad description but I havent found any ways to pin it more down to anything... hopefully I am not the only one experiencing this.

The only other maybe useful information I have is, that the recorded footage is dated from back over 2 years ago and the most recent clips recorded just a few days ago.

So maybe Premiere has trouble dealing with such a wide time frame? But again it was all recorded on the same device so that can't really be the issue. 

The pproj. file was created only 2 months ago, so that itself is not that old.