this is normal.
when you join a channel, you collect a record of all the links being shared in that channel. As others come and go, your client then feeds part of that record/index to others.
Some BW is also related to browsing. If someone browses the links you may choose to share, some BW will be involved in that too.
Also, just maintaining channel connection, since it is a p2p mesh, not a client/host type of connection, will take BW.