The sound may be coming/transmitted from somehere else, strange but true. Try checking bolts, nuts, clamps etc elswhere on the bike.
Do not grease your crankarms, (as mentioned above), where they interface the spindles. More than one manufacturer requires that those surfaces be CLEAN and DRY, even cleaning with acetone is recomended to remove ALL grease and other comtaninants!!!!
If you grease the spindle flats it is very likely and easy to overtighten the crankarm. I learned this when I was working for one of the best and most respected shops in the nation, we used to get calls from customers from all over the world!
If the BB is a Shimano sealed bearing unit, they they have in the past, recommended the putting silicone seal on the BB or cup threads.