I live about two miles from J7. There is an aroma to that junction, not consistently but reasonably often.
It’s certainly not Holland’s Pies, that’s at the other side of town totally. It -could- be Whinney Hill tip, but I don’t think it is – if you drive up towards the tip then the smell dissipates, and the tip itself doesn’t smell particularly strongly most of the time anyway.
The only other thing I can think of round there is that might be a contender is, the canal runs right next to that junction. That can be whiffy occasionally.
There’s not much else nearby that jumps to mind really. There’s a posh hotel round the corner so it could be their kitchens I guess, and there’s a small industrial park across the way so it could be something on there I suppose.