17.5 tecumseh making a weird noise

I have had this Murray for about two years and I have completely built it up into a 40 mph all terrain mower. Ever since I bought it, it has made this weird noise, almost like a rattling or I don’t even know. I straight piped it a year ago and it is un governed. It is still making the noise, i can’t really tell what it is I know it is common for tecumseh motors to be loud. It does not have any loss of power, it runs perfect and there is no metal shavings in the oil, and it only burns oil every once and a while if it sits on a hill facing down hill on startup. I am running a wix filter with Lucas 10w30 oil that is advertised “for wet clutches” I do not know if that has anything to do with it. I have not changed the oil since last year so it is due for a change. It gets very hot where I live too. I do not know if these are all factors. It has a dirt bike carburetor on it. Brand new spark plug. Could it be the valve lash is off? Or is it more likely excessive wear in the crank bearings

Might not be internal either...maybe something isn’t bolted down right?

I will make sure the mounting bolts are tightened all the way. If it keeps going after that should I run thicker oil?

I was thinking loose governor parts or gears rattling around. Don't run thicker oil. Use the oil specified for the engine.

Tightened all the bolts down, still no luck. Will it kill the engine to keep running like this or can I still use it how I always have? Thanks!

I’m gonna try changing the oil and filter and see how that works and maybe I’ll put some zinc additive in it. If that doesn’t help I’ll pull it

I have another motor I saved as a possibility to put in this Murray, it is a 14.5 I/C Quiet Briggs. I have not put it in yet though because I was thinking of that motor as a downgrade from this one because it is not pressure lube. Does it make that big of a difference if the motor is pressure lube or not?

Not really. It won’t last as long in the long term before needing a rebuild, but as long as you change your oil that is really far off in the distance.