Is there any rate limt for api access? #278

Dear support,
My app sometimes receives the error 409 when sending multiple creation requests （total ～16 requests in a minute, 3~4 failed）to the tripIt API. The failed requests sometimes just get passed when I replay them more times. So status code 409 looks like represents the "Too Many Requests" situation for TripIt API.
And If there is some kind of rate limit on the TripIt server-side, what's TripIt's suggestion for the volume and frequency of requests sent by the client APP?

Best Regards
Yan