25 March 2016
If the notice has come from the local AO, a reply stating the facts should suffice. However, it is not clear if the interest of 40,000 is on savings bank account or on SB and Time deposits. If it is from SB, apparently huge balances have been lying in the account and / or deposited and that is the cause for issuance of notice.
The IT Department is entitled to investigate the surce of funds of any person assessee or non assessee and in your HUFs case there is also a PAN card.
This advice may vary depending on the facts of the case.