The quality of the HDMI cable makes a big difference...
In all likelihood it's the cable. I've seen this issue personally and replacing the cable fixes it.
What OS? There are driver issues in Win 7 causing this behavior.
This message was posted on behalf of Intel Corporation
For better understanding:
Is it happening with the two HDMI ports?
Have you tried with a High-speed HDMI cable?
Let’s try doing a Graphics Driver Update using the adapter.
-Access the device manager (you can use windows start searching to find it).
-Look for Display adapters double click on it.
-Right click on your Intel® HD Graphics and hit properties.
-Go to driver tab and hit uninstall.
-Select "Delete the driver software for this device"
After that install the latest Intel® HD Graphics
Please let me know the outcome.