a noise reducing groove formed at an upper surface of {HEAD ~ the pump cover} and having {TAIL ~ a predetermined length}; and 
a noise reducing groove formed at an upper surface of { HEAD ~ the pump cover } and having { TAIL ~ a predetermined length } ; and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH