If it's a new thing, I'm just wondering if your waste plumbing was done properly? There could be a blockage because of how it's been set up, or if there's not a proper functioning waste trap in, smells from the drains/sewerage come back up the pipes. I think a lot of washing machines are connected to drain under the kitchen sink, and share that trap, though some (like mine) have their own standpipe and waste trap behind them. If you aren't sure what to look at or check, I'd definitely get someone to come have a look at how your drainage is set up, and that all is OK with it