not sure if my imagination or not but when riding it kind of feels notchy or like riding over little bumps if that makes sense? Kind of hard to explain Could this be bairings?
What wheel is it? If its just rumbling best bet to remove wheel and spin bearing by hand you can normally feel or hear its notchy. In other cases it will fail in use and you will defo know something has gone wrong then check wheels in situ and you will be able to rock wheel side to side.
For peice of mind for you yes but will cost you. You can go to a bearing supplier and get good quality bearings much cheaper also sometimes OEM are specials so get the bearing numbers and phone around. I would check bearings and that your not down to metal in your pads as this is a similar feeling but normally only when ur on the breaks. Check also ur chains lubed and not tight.
With me it was when my back wheel moved 2 inches either way on the axel lol Scared the shit out of me on my old cbr400rr
Be careful what bearings you buy . A lot of Chinese shit out there with English sounding names. Buy Koyo, FAG , European makes. Best way to check bearings is remove wheel, stick thumb in hole and turn it. Should be smooth with no notchiness. If in doubt , replace, but take care replacing em, do not apply any load to the bearing INNER race, only the outer.
Martin, grab the wheel at 5 o'clock position and 11 o'clock position and try to twist the wheel, if the bearings are pooped you'll feel movement in the wheel, if the bearings are ok there will be no movement. As the other guys have said there are some crap bearings on the market for sale.