If it was a muffled thud, then most likely it wasn't a hit. A direct hit tends to sound like more of a 'crack' sound. Also, if it's very close or a direct hit - you can often smell the ozone created.
A majority of strikes do no damage particularly on the newer aircraft which have the technological advancements to reduce the damage. In particular, Airbus FBW types have to have very good screening/bonding to protect their flight control systems. But damage can occur and on the A320, the exit points tend to be the engines and many of our aircraft have blended out small sections of the jetpipes missing.
I have had many strikes and only one caused significant problems. This was an older 1960's jet and it tripped off one electrical system, blew the radars and half the radios. Both pilots also felt a shock - the FO through his feet and I through my left foot and up the left side of my body to my left hand which was pressing the transmit switch. And on a 747 once, the strike entered the airframe via a windscreen wiper - which promptly vapourised. As this happened about 18'' in front of my nose - it got my attention!