Loud hvac air return. Loud blowing air and fan noise. How to fix?

In my home the air filters are located just inside of the two large return air registers. When I installed “better” (I.e. more restrictive) air filters, the noise from the air being pulled in increased dramatically to the point of being annoying. I also realized it was putting a large burden on the fan motor which was not designed to pull against that much of a restriction. I installed a less restrictive filter and brought the intake air noise down to an acceptable level. The manufacturers use a numbering system to rate their filters for efficiency (and hence restrictiveness). Most use the MERV# but Home Depot uses an FPR# and 3M uses an MPR#. They are different values but it is possible to convert between them (do a search on comparing them). Perhaps this info might help solve your problem. Good luck.

Edit: This concept/issue would be the same for a filter installed right at the furnace as well. If the filter is too restrictive, the noise will travel back up the ducting to the intake vent producing the same problem.

How do I check what level the fan is on? Please and thank you!

there already is a filter inside the return air box right near the unit

i didn’t want to add another filter behind the grill for fear of restricted air flow

can another filter be added behind the grill?

would it quiet down after that?

if so,what type of filter to use?

Not sure. If it wasn't that way it might restrict airflow too much.