DA-40 avgas or DA-40 TDI? I find the TDI with a silencer quieter than a PA-28-161 with a silencer but not by much.
Some data from
www.texelairport.nl -> go to visitors
PH-SVI, a PA-28-161 with a silencer exhaust (the long tube kind) 72.8 dB
PH-SVH, a PA-28-161 with a muffler in the exhaust pipe 74.7 dB
PH-SVR, a DA-40 TDI with the factory silencer exhaust 69.5 dB