Well the car got through the MOT again this year, with no reference to the knocking. So with everyone suggesting front suspension top mounts, or anti roll bar bushes, but with WMSS having found nothing wrong with these earlier in the year, I asked on the Facebook Saab 9-3 group whether it might be engine mount related.
One guy suggested up open the bonnet and get someone to start the engine and rev it up. If the engine kicked backwards significantly, then it could be the bottom mount on the rear of the subframe could be at fault, but that if it was, it was a cheap part and an easy job to change.
So this evening, I allowed the missus to sit in the driver's seat of Jet for the first time ever, with the key in her hand (dangerous, I know, but I gave her the benefit if the doubt
). I got her to start the car and then rev it up a few times. Surprisingly the engine did not really kick back, but I think I may have spotted what the issue may be.....
As she started the car, the whole air filter box, and the pipe back to the back of the engine shook. I thought, that didn't look right. On closer inspection, the air filter box appears to have no securing fixing at the front, and seems to be resting on the engine mount housing. Looking underneath, it is also not connected to the dirty side intake pipe that disappears down into the wheelarch area. The result is that the air filter box is rattling around held on by two fixings at the back, but not secured anywhere else!!
At the front down above the longitudinal, there appears to be some sort of rubber mount, that could form part of a fixing for the air filter box, but there is nothing in it, and certainly nothing extending from the filter box that could be part of a mount. So the question is, do I need a new air filter box?
The photos in the Haynes manual are very poor, and I can't see what the box is supposed to look like, even less how it is supposed to be installed.
I'll try and post some pics/video, if they are not too big...….