Rattle noise in engine

2006 Honda civic dx, manual transmission:

when accelerating, sometimes, I will hear a rattle in the engine. I let off the gas and .01 seconds later it is gone and continue going. 30, 50, 70 mph, no real noise, then sometimes when a cruising at speed for 4-5 seconds I may hear it, the let go and it stops, then go again and might not hear for about 2 minutes, then may hear it again. long story short it is a rattle and I am just making sure not detrimental.

I was going to add a additive today, but have heard it may be a bearing or a rod going. but I feel that it is too inconsistent and those, I can floor it and or drive normal and the pistons are firing and smooth, then once ins a while a noise.

thanks so much !