Funny thing a while back. We bought one of the very first GMC Duramax trucks that was built, and it had this little "tick" in it when idling right from brand new. It now has over 300,000 on it and still runs like a charm. It still has it's idling "tick" and that hasn't changed. Apparently all of the first generation Duramax engines had this occasional "tick" when idling. GMC came up with the conclusion that the "tick" was caused by the engine oil gettng bubbles of air in it and making noise at the rod bearings as the bubbles that were entrained in the oil exploded.
So, when the second generation Duramax came out in mid-2003, it had a revised oil pressure-regulation system. Apparently GMC had lowered the oil-pressure and increased the oil-flow. This got rid of the "tick" at idle. We always have used 0w40 synthetic oil in that '01 Duramax, year-round since it was new. That little "tick" has never changed no matter what brand of oil was used.

But, Doc Shadow is correct about Yamalube oil being bad for air-entrainment in air-cooled motors. Even my Kubota Generator motor was noisier with that stuff in it.

A Roadstar has four valves per cylinder too, that many valves must constitute for a little more noise, wouldn't it? My Roadie's valves make noise, but are not excessively noisy. You have to remember that Roadies do not have a water-jacket around the cylinders to dampen any engine noises.