I have a RB750G running 4.x RouterOS. I'm having a problem with my sip trunk provider seeing my local ip address on there end so I get one way audio. How can I, or can I have the router NAT the Sip header?

Thanks in advance.

RouterOS SIP helper is available at /ip firewall service-port, however it is enabled by default.

Thanks for the reply, however I have check that and it is enabled. Is there anything else I can look at?? They showed me the sip head and it clearly shows my local ip address.. Thanks for the input.

Have you tried disabling the SIP profile in the firewall?
I had this exact same problem, and turning it off took care of it.

I have yet to see a SIP "helper" that actually worked correctly (MikroTik or otherwise), particularly if your service provider is already trying to do NAT traversal on their side.