Syn attack

Hello freinds

I sniff one camputer in Our Network using wireshark and I have this log :

jwalkserver > bmc-onekey [ACK] Seq=2669 Ack=141165 Win=65535 Len=0
navbuddy > bmc-onekey [ACK] Seq=3814 Ack=18105 Win=65535 Len=0
pe-mike > bmc-onekey [SYN] Seq=0 Win=65535 Len=0 MSS=1460 SACK_PERM=1
boomerang > bmc-onekey [ACK] Seq=534 Ack=213 Win=65323 Len=0
sftsrv > bmc-onekey [ACK] Seq=427 Ack=146 Win=65391 Len=0
h323hostcallsc > bmc-onekey [ACK] Seq=4737 Ack=103611 Win=65535 Len=0
telesis-licman > bmc-onekey [ACK] Seq=594 Ack=156 Win=65380 Len=536
dbreporter > bmc-onekey [ACK] Seq=1218 Ack=308 Win=65228 Len=536
elan > bmc-onekey [ACK] Seq=2408 Ack=621 Win=65535 Len=536
checksum > bmc-onekey [ACK] Seq=1 Ack=1 Win=65535 Len=0

The distination is our proxu server in port 3561

I would liek to find the source of this problem because this PC is sending a lots of syn attacks to our gateway using our proxy port

Thank You