Check all bolts under the hood, especially anything attached to the firewall. I had a nasty vibration in my WRX from the time it was new, the dealer finally found it, it was a loose bolt on the firewall. Sounds similar to what you are describing.
Check all bolts under the hood, especially anything attached to the firewall. I had a nasty vibration in my WRX from the time it was new, the dealer finally found it, it was a loose bolt on the firewall. Sounds similar to what you are describing.