P2599'2 buzing relay

Hi,
I have mounted the kit and made several tests.
However, I have each time the same issue: the wipers are running as per the manual (goes on and off according to time delay setting) but when the wipers are just starting to move, i can hear the relays buzzing.

Is this normal?
Can I let this as is?
Can you tell me what is the closing time of the relay?
Do I have to change the closing time of the relay?
Thanks in advance for your reply.

here is the link to the wiring diagram modified with the P2599’2 circuit:
docs.google.com/open?id=0B9eWn5 … F81WVdMb0E

Adding a large (4700µF) cap over the kit power supply can help to keep the power stable.