well at around 1200-about 1600 rpm is when i hear it. its never at idle, the idle is sound is the piston slap, its coming from around the left bank, but like i said its a valve train issue. but only really there when i use quaker state QHP. it is 5-30. i get the best MPG with this oil but i think i may need to run lucas additive or something. (which i dont like)
oh and yes i do tow with it, up to 11000 lbs before. its pretty regular that it gets at least a 4000 lb load once a month and the 11000 lb load once or twice a year. plus any other load when i want to take four of the six horses out.
If you only get the noise with qs, don't use qs.
Adding Lucas to it will only degrade the quality of the oil further and cause foaming.
Try some Valvoline, their 5w30 tends to run on the thicker side.
If your doing regular towing I would just stick with a 10w30 as your oil will run hotter and tend to shear faster.