Dear SND,

Flow Induced Vibration is a low frequency vibration (typically below 50 Hz) generated by high kinetic energy Rho.V^2 and high mach number, meanwhile acoustic induced vibration is a high frequency vibration (500 hz-2000 Hz) generated by high pressure drop coincidence with high flow rate.
Physically you can see the piping system vibrate for phenomena of FIV but for phenomena AIV you will not see it vibrate physicly but you only hear a high noise generated by the high frequency. AIV also called shell mechanical vibration as the inner shell of the pipe that vibrate circumferentiall and radially.
AIV always hapened in gas system, while not for FIV, AIV can generate failure within minute (not days or weeks) but FIV can take days.

Read EI 2nd 2008 for detail LOF assessment, and visit Internoise website to get latest INTERNOISE 2012 papers related to new approach and method for evaluation AIV throug FEA and LOF or combination of both.

Regards