9.75% SENIOR NOTES DUE 2014 THIRD SUPPLEMENTAL INDENTURE

Exhibit 4.56

XM Satellite Radio Inc.

9.75% SENIOR NOTES DUE 2014

THIRD SUPPLEMENTAL INDENTURE

Dated as of March 6, 2009

The Bank of New York Mellon

Trustee

THIRD SUPPLEMENTAL INDENTURE, dated as of March 6, 2009, by and among XM Satellite Radio Inc., a Delaware corporation (the “Company”), XM Satellite Radio Holdings Inc., a Delaware corporation (the “Parent Guarantor”), XM Equipment Leasing LLC, a Delaware limited liability company, XM Radio Inc. (the “Subsidiary Guarantors”), and The Bank of New York Mellon, as trustee (the “Trustee”).

WITNESSETH

WHEREAS the Company has executed and delivered to the Trustee an Indenture dated as of May 1, 2006 (as amended and supplemented, the “Indenture”), providing for the issuance of 9.75% Senior Notes due 2014 (the “Notes”);

WHEREAS, in connection with an offer to purchase undertaken by the Company for the Notes (the “Offer to Purchase”), the Company commenced a solicitation of consents from the Holders to certain amendments (the “Proposed Amendments”) to the Indenture set forth in the Offer to Purchase and Solicitation of Consents of the Company dated July 29, 2008 (the “Consent Solicitation Statement”);

WHEREAS, this Third Supplemental Indenture evidences the Proposed Amendments described in the Consent Solicitation Statement;

WHEREAS, Section 9.02 of the Indenture provides, among other things, that with the written consent of Holders of a majority in aggregate principal amount of the Notes outstanding (the “Outstanding Amount”) voting as a single class, the Company may from time to time amend or supplement the Indenture, subject to certain exceptions specified in Section 9.02 of the Indenture;

WHEREAS, on July 29, 2008, the Company mailed or otherwise delivered the Consent Solicitation Statement to each Holder of record as of such date;

WHEREAS, the Holders of a majority of the Outstanding Amount have consented to the amendments effected by this Third Supplemental Indenture in accordance with the provisions of the Indenture;

WHEREAS, this Third Supplemental Indenture has been duly authorized by all necessary corporate action on the part of the Company; and

WHEREAS, the Company has delivered, or caused to be delivered, to the Trustee an Officers’ Certificate and an Opinion of Counsel meeting the requirements of Sections 9.06, 12.04 and 12.05 of the Indenture and stating that the execution and delivery of this Third Supplemental Indenture is authorized or permitted by the Indenture and that all conditions precedent (including any covenants compliance with which constitutes a condition precedent), if any, provided for in the Indenture relating to this Third Supplemental Indenture have been satisfied.

NOW THEREFORE, in consideration of the foregoing and for other good and valuable consideration, receipt of which is hereby acknowledged, the Company, the Parent Guarantor, the Subsidiary Guarantors and the Trustee mutually covenant and agree for the equal and ratable benefit of the Holders of the Notes as follows:

ARTICLE 1

AMENDMENTS

SECTION 1.01  Deletion of Certain Definitions . Sections 1.01 and 1.02 of the Indenture are hereby amended by deleting the definition of each term that is used in the Indenture only in the Sections thereof that are deleted pursuant to Section 1.02 hereof.

SECTION 1.02. Deletion of Certain Sections . Each of the following Sections of the Indenture is hereby amended by deleting the text of such Section in its entirety and replacing such text, in each case, with the words “Intentionally Omitted”: