Hanover bars: Should they always look the same?

[KingBuZZo]

So I'm transferring the same PAL VHS tape over and over again and it always gives me a different "level of intensity" of Hanover bars. Shouldn't they always be the same? Sometimes they are barely there, sometimes they're clearly visible, in another case, they're again clearly visible, but look different than before.

Could it be an issue with my VCR?

I can also upload AVI clips if it's easier to identify the problem (or whether there even is one).