Yes - but I think those are either contractions (なければ → なきゃ or なけりゃ) or slang or colloquialism (わからない → わかんない or わかんねぇ~).
I get the feeling from the example mentioned, that the OP is imagining something other than the above. Maybe he/she is hearing a number of things not found in the textbook, and is looking for a universal, easy-to-understand rule.
Hopefully the good Dr. LunatiKk will come back and shed a bit more light!