Whining

Coming home from Truro the other day I noticed a whining coming from the engine. Once home I lifted the lid and listened. It was high pitched so i thought it might be the alternator. On the internet all sorts of possible causes were put forward, a simple one that could do no harm was to check the charging as apparently when over charging they can whine. Much to my surprise I found a suitable earth strap and terminal at Halfords, one past the polish, toys, radios etc.
I fitted it and the whine was gone; but not for long. As the car came back the whine reappeared. The alternator was less than a year old i have just replaced the distributor and water pump. surely not the alternator already?
I took it to my garage, Phil listened and said he had found the cause, when he pressed down on the air filter the whining stopped.
He offered to drive around sat on it as a cure but a brick wedged between it and the engine cover did the trick just as well and formed an impressive "power bulge" in the engine cover, a bit like an E Type.

No; I am in fantasy land there but when I got home, not far, I got the spanners out to see if anything was loose.
The nuts holding the carburettor on were not even finger tight, you could spin two with the tip of your finger.
Well done Phil! I tightened them up, they had been tight six months ago but? People say do not over tighten these nuts. A fine balance.
The whining has gone.