Portable benchtop planers are pretty noisy. They use
universall motors which put off a high pitched whine.
Japanese 110v jointer/planer combos use those
motors too.

Other than that, jointers aren't generally very noisy.
Planers are louder. Your dust collector is going to
make some noise too. I had a Robland 12" jointer/planer
combo and it wasn't too noisy up close due to all
the iron and steel in it I think. I wore hearing
protection when using it, but I think cutting plywood
on the table saw was noisier.

Turn on a router table, walk out of your shop and
you'll get an idea what the sound of a portable
planer will be for your neighbors.

 

i was shocked at how much quieter the 15" grizzly w/ spiral head was compared to the 13" Dewalt DW735. After I had the planer for a while and was so pleased with the spiralhead, I thought I would switch my 8" jointer over to a spiral as welll. Im sure its a bit quieter, but not near the different as the planer.

 

Any jointer or planer with a spiral type cutter head will be quieter then a blade type. If you are looking for the quietest then look for this type of head in the units. In a small shop the jointer/planer combo machine is a great deal, both in cost and in the space that is required. What is your budget for these machines, as spiral heads are more expensive?

 

Induction motors in bigger machines like jointers will be (much) quieter than the universal motors used in lunchbox type planers. That being said there are differences between brands, and between newer and older tools. For example my Makita lunchbox planer is quite a bit quieter than a Delta I used to have.

Same for routers, the Triton I have now, mounted in a table, is much, much quieter than the Hitachi I had before, which was a real screamer.

Personally (and I think unless your budget is huge and you can afford the top of the line) I would definitely avoid buying a jointer/planer combo machine. Very impractical in my opinion as those 2 functions, along with the table saw, are frequently used together when dimensioning wood. I used to own that combo that Rikon sells (under another brand though), and hated it, cheap and a hassle to use.

The loudest machine in my workshop now is the shop vac…it's louder just turned on than any of the woodworking machines when they are being used. Hmmm, the hand held circular saw is loud too but I don't use that very often. A power miter saw might be louder yet but I don't have one…

 

What is your workshop setup like? Make sure the building has sufficient insulation, put insulation on the backs of doors/garage doors and keep them closed when working with loud machines, and unless you're physically sharing a wall with a neighbour's living space you'll probably be fine.