Re: Odd sound from engine.
I also would recommend to use a synthetic 5W30 of a known brand oil company.
I have used several brands in mine and had the valve cover off last week and was surprised how clean the internals where after 162.000 km. No sludge at all and all clean and shiny. I want to pull my oil pan soon to check if the oil pump screen is clean as well.
Regarding the use of Seafoam, you have to check regulary the color of the oil, if it gets darker rapidly, you better change it soon, because the seafoam is doing its job and is removing sludge and other deposits.
I don't think any additives are necessary to mix with the oil.