Yeah I feel you man, but it's only normal.
Imagine all those geeks/rip fanatics/weirdos who took the time and the risk to buy/steal/leak albums and rip them for you and put them on the internet, which might land them in prison sooner or later, all this for your pleasure and "money saving" should I say...
What do you think is in for them???
Recognition of course. So those groups always take the liberty to tag the files with their name or with something that's important to them. And the "smart" ones would tag them in a way that's really annoying and time consuming for those who download them to erase the tags.
Just take the time to correct them one by one and be thankful that you got all this stuff for free without spending a cent of your hard earned money...
Peace...