Thicker can reduce the noise, but i personally wouldn't want to put anything thicker than a 10w?? grade in it, this shouldn't make a major difference to your tappet nois as a result I would carry out the basic stuff mentioned above like ensuring the oil ways are clear etc.
It may be an idea to use your currently oil change as a flush, do around 500miles on it and then change it again. (no point in changing now as you've just put it in).
As for flushing agents, I use Forte (trade product, available from garages that stock it), or Wynns/Millers. I don't suffer any issues using these on my 328i and have done so for the past 3-4 years. My oil is changed regularly so it never builds up any deposits etc that I feel can clog oil ways etc.