Well, typically Ti is not one of the isotopes more susceptible to interference (polyatomic, isobaric, etc.) however anything is possible, and it would depend on the ICP-MS that you are using, the age, the conditions of the cones, etc.
I would lean more towards the reference standard that you are using. Ti is not very stable when mixed with other isotopes, which is why you will have a difficult time finding it included in many of the multi-element reference standards available from places such as CertiPrep, VHG, Perkin Elmer, etc. It is also why the leading supplier of PT samples for EPA certifications, Environmental Resource Associates, makes sure that they separate out Sn and Ti from the other elements in the PT sample, and you receive a separate sample for those two isotopes.
So I would start there. Can you tell us how you are preparing your calibration standards as well as how many isotopes you are scanning for at one time...or at least how many other isotopes you are calibrating for when you are analyzing for Ti?
Also some more info on the type of instrument you are using might be helpful as well...in the event it is not an issue with your reference standard.