Insert Trigger on Linked Server during a FULL DB Backup

I have two servers, Server A and B. Server B is linked to Server A as a linked Server and there is one table TableA on ServerA and ServerB.
TableA receives contineous Inserts and there is an Insert trigger written on TableA on ServerA to insert the same data to ServerB using the INSERTED table. This equation works fine for most of the day, but whenever I run a Full Database backup on ServerB, the whole Trigger Insert process slows. I wonder why? Any idea, any suggestion?During backup server is kind of busy ;) and if there is only one processor and not fast I/O device ...