My wife wants to know what the noise level is in the sidecar. Do you have a DB meter?
I don't have one.....maybe if the iphone has a app for it I can get you something. If you can do the research if there is a APP for that I'd be happy to try it for you. It may be a week or two as I'm out of town on Business.
The answer from my wife is: "it depends".....! I have 4" Rineharts...which are LOUD...they ping off the Sidecar, but not so loud that your eyes or ears would bleed. My wife wears ear plugs just to reduce the "general noise". If she forgets to put them in she knows it, but it's not like being on the back of the bike....so quieter than that. There is very little wind noise with the shape of the canopy. This is the same shape as our Goldwing (she didn't wear plugs in that one ever) and protects you very well. So.....the pipes are the biggest factor for noise. Even with the pipes it's not so loud that she can't use our SENA Headsets (for a frame of reference), she can even use her phone (paired up via bluetooth with the headset) while driving on the Highway at 70 (speaks volumes at the noise canceling capabilities of the SENA headsets). She uses a 'wrap around' style that she can wear without a helmet or with a 1/2 helmet.
http://www.revzilla.com/motorcycle/sena-sph10-bluetooth-helmetless-headset-intercom.
The answer to the question you didn't ask: I feel the "popping" of the wind on the bike is worse for your hearing than the noise from the bike, and she wouldn't have any of the wind pressure/popping on the ears that you'd get on the passenger seat. I wear a 3/4 helmet and no ear plugs and it's fine. I wear this helmet and headset:
http://www.revzilla.com/motorcycle/bell-mag-9-sena-helmet-solids If I'm not wearing a 3/4 I have "molded" ear plugs for a 1/2 helmet. Even on the Goldwing, where noise wasn't the issue, I felt my hearing being effected by the wind on long trips and started wearing ear plugs and then switched to a flip up helmet and that stopped the wind issue.
If you wore a 3/4 Helmet, ear buds, or plugs in the Sidecar that would probably be enough even with the pipe issues. If you have stock pipes, I'd bet you would be fine without any extra hearing protection. It is definitely not LOUDER than being ON the back pillion!
I hope that answers your question.